The invention is directed to a method for the recovery of steviosides from dried plant raw material of Stevia rebaudiana Bertoni by extraction and purification, undesirable impurities being removed by chemical treatment and the purification being accomplished with anionic and cationic exchange resins.
Steviosides are used as serviceable artificial sweeteners and are added to low-calorie foods or as replacement for natural sugar. Artificial sweeteners were developed for use by diabetics and to decrease the calorie content of food preparations, especially for a low-calorie diet. These sweeteners are frequently sweeter than natural sugar and may, in order to achieve the same measure of sweetening action, be used in small amounts. Numerous sweeteners are synthetic in nature, for example, saccharin, cyclamates and aspartames. The use of some of these is prohibited or limited, because pharmacological investigations have shown that they can produce cancer. On the ohter hand, the steviosides are fully usable and have shown no disadvantageous effects in clinical trials.
Conventional methods for the extraction and purification of steviosides are associated almost exclusively with the use of organic solvents, such as methanol, ethanol or ether, and many require that the steviosides be absorbed at first on a resin with subsequent elution with an organic solvent. The concentrated, evaporated solutions from this method usually are treated with methanol or ethanol to bring about the final crystallization of the end mixture. Other methods make use of iron or aluminum salts to remove impurities. These two materials require a further treatment with sodium hydroxide to remove residues of the iron or aluminum salts.